textproduct: Rapid City

KEY MESSAGES

-A blocking pattern will support a ridge of high pressure over the CONUS this weekend into next week, supporting very hot temperatures and elevated fire weather concerns

-Thunderstorms will be possible at times this weekend into next week as monsoon impulses advect around the ridge and into the region

UPDATE

Issued at 955 PM MDT Thu Jul 23 2026

Shower/storm activity has largely diminished across the CWA with only a few spotty light radar returns over western SD. Water vapor imagery shows dry air moving into the region with the monsoonal moisture now to our south. Conditions downright muggy tonight with dewpoints in the 60s to near 70 across much of western SD into northeastern WY. With the ample low level moisture, light winds, and clearing skies overnight we could see some localized fog develop in the river valleys over the western SD plains, but potential coverage not enough to warrant mention in the grids.

Much hotter for the weekend as upper ridge strengthens over the Northern Plains. Still looking like much of the western SD plains will hit the triple digits for Saturday through Monday with advsy level heat indices expected. In addition to the heat, monsoonal moisture will still advect into the region, supporting the development of high-based storms Saturday afternoon as weak wave moves across the area.

DISCUSSION

(This Evening Through Thursday) Issued at 1232 PM MDT Thu Jul 23 2026

Upper level ridge over the Rockies will shift east and expand over the central CONUS. This will result in very hot temperatures this weekend into next week. Departing batch of monsoon moisture will support scattered showers and storms into the evening as diurnal heating allows for expansion in coverage this afternoon. Locally heavy rainfall will be possible given high PWATs and slow movement. Upper ridge will begin to shift east Friday although a ridge topping impulse will shift a trough across the southern Canada and the Dakotas, with the tail end of the trough stalling in the FA later tomorrow. Much warmer temps tomorrow with highs in the 90s most places, with a few low 100s possible in areas on the Plains. Aforementioned upper trough may support a few isolated showers or storms across NW SD in the afternoon, carried a low pop for this. Separate weak impulse may also support a shower or storm across northeast WY in the evening and so have also added low pops there as well. Upper ridge will shift east Sat with very hot temps expected. Highs will reach 100 or higher for most locations on the Plains, supporting adv level heat index readings. Low level moisture will deplete some with mixing, but sustained southerly flow will prevent the BL from drying out too much most places. This will help keep heat index readings higher, esp over central SD. Heat looks to persist at least through Tues, possibly longer depending on how passing ridge periphery impulses affect the ridge. Expect that there will be TS chances at times in this period as monsoon moisture advects around the NW side of the ridge. This includes Sat when another monsoon wave will advect around the ridge in SW flow and into the FA later Sat, supporting high based TS chances. Gusty winds will be possible with any thunderstorms in this period given high based nature and near inverted-V profiles. Ridge will retrograde back west some by mid next week, supporting slightly cooler but still hot temps, with expected TS chances as the lee trough interacts will passing impulses.

AVIATION

(For the 12Z TAFS Through 12Z Saturday Morning) Issued At 528 AM MDT Fri Jul 24 2026

Patchy morning fog has popped up around the area. Looking ahead, the fog should fade out over the next 1 to 3 hours. Then, VFR conditions are expected throughout the forecast period.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.